FORCE MEASUREMENTS ON A HYDROGEL WITH AN SFM

A scanning force microscope (SFM) has been used to measure the force i nteraction between a pyramidal silicon nitride tip and a dextran hydro gel immersed in PBS solutions with various concentrations. The dextran gel was attached to a gold surface via alkane chains. Samples with on ly alkane chains attached to the gold surface served as a reference an d gave force-distance curves consistent with a double-layer interactio n. The obtained force-distance curves depend on the buffer concentrati on and can be used to estimate the gel thickness. It was found that th e gel was around 190 nm thick for buffer concentrations lower than phy siological and about 140 nm for physiologic buffer. A tentative explan ation is given to this observation. (C) 1995 Academic Press, Inc.